1. Field of the Invention
The present invention relates to a composite material which is suitable for controlling the physical properties of the surface and interface of a solid article such as wettability, adhesive property, surface energy and the like, for improving dispersibility, chemical resistance and the like, for preventing adhesion of a contaminant, for preventing electrostatic charge, for imparting functions such as electrical conductivity, photoelectric conductivity, thermal conductivity and the like, and the like and which is available in a wide range of field including a paint, cosmetics, a protecting film for an electrical part and a mechanical part, a photoconductive material, a catalyst, a photo-semiconductor such as a photo-catalyst, a photoelectric conversion material and the like, a filler dispersion type composite building material, an additive for a toner, and the like, and a method which can produce the above-described composite material efficiently.
2. Description of the Related Art
As a method for producing a composite material in which a thin film is formed on a substrate, a casting method and a spin coating method are conventionally known. The casting method is one in which the composite material is produced by applying a solution prepared by dissolving a compound in an organic solvent and the like onto a substrate and evaporating the organic solvent. The spin coating method is one in which the composite material is produced by dropping a solution prepared by dissolving a compound in an organic solvent and the like onto a substrate revolving at high speed and by removing excess amount of the organic solvent.
However, in these methods, controlling of film thickness at molecular level and controlling of molecular orientation are difficult, and functions which a molecule inherently has cannot be manifested sufficiently.
As a method for producing a composite material which can control film thickness at molecular level and molecular orientation, Langmuir-Blodgett method (hereinafter referred to as LB method) is known. The LB method is one in which the composite material is produced by spreading molecules having a hydrophilic terminal group on the interface between a gas phase and a liquid phase (water), forming a thin film with keeping the area occupied by the spread molecules minimum, and transferring this thin film onto any substrate. Since water is generally used as the above-described liquid phase, the molecule having a hydrophilic terminal group is oriented so that the terminal group is directed to the liquid phase (water). In the LB method, to keep the area occupied by a molecule minimum, an instrument called a barrier is used to push one end of the interface between a gas phase and a liquid phase (water) to decrease the area occupied by molecules for increasing molecular density. By this procedure, a monolayer can be formed on the interface between a gas phase and a liquid phase. By transferring this monolayer onto a substrate, the composite material can be produced having a monolayer of which molecular orientation is controlled at molecular level.
However, though the LB method is an excellent method in view of molecular control, since bonding strength between the monolayer and the substrate in the resulted composite material is extremely weak, there are drawbacks that the composite material has poor mechanical strength, has weak heat resistance and is lacking in durability. As a result, even if a thin film composed of a functional molecule of which molecular orientation is controlled is formed on a substrate, the function thereof is not fully manifested. Further, like a casting method and a spin coating method, there is a problem that a thin film can not be formed on a substrate of which surface is not smooth such as a fine particle and the like, so that the shape of a composite material is restricted.
As a method which can solve the problems in the LB method and provides a composite material having excellent function, a chemical adsorption method is proposed. As the chemical adsorption method, for example, there is known a chemical adsorption method using a chemical adsorption molecule composed of a chlorosilane-based compound and the like suggested by J. Sagiv et al. [J. Sagiv et al., J. Ame. Chem. Soc., 1, 92 (1980), J. Sagiv et al., J. Am. Chem. Soc., 105, 674 (1980)]. Above-described chemical adsorption method is one in which the composite material is produced by forming a monolayer on a substrate by utilizing the condensation reaction of a reaction group exposed on the surface of the substrate, for example a hydroxyl group with a hydrolytic functional group on the end of an adsorbed molecule.
In the chemical adsorption method, the constituent molecule of the monolayer chemically reacts with the substrate to form a chemical bond such as --Si--O--, --Ge--O--, --Ti--O-- and the like, and therefore, there can be produced the above-described composite material comprising a monolayer having high mechanical strength, excellent heat resistance and excellent durability. In the chemical adsorption method, an adsorption molecule having a thiol group can be used instead of the hydrolytic functional group. In this case, since the constituent molecule of a monolayer reacts with a substrate to form a covalent bond with --S--, the composite material comprising a monolayer having high mechanical strength, excellent heat resistance and excellent durability can be produced , similarly to the composite material using an adsorption molecule such as a silane-based compound, germanium-based compound, titanate-based compound and the like.
Further, in the case of the above-described chemical adsorption method, since a thin film can be formed also on a substrate of which surface is not smooth such as a fine particle and the like, a wide variety of shapes of the above-described composite material can be produced, and the composite material obtained can have a wide variety of applications.
Therefore, there have been attempts recently to produce the above-described composite material in which a functional molecule is introduced on the surface of a substrate by utilizing the chemical adsorption method. Japanese Patent Application Laid-Open (JP-A) Nos. 2-110172, 6-214420 and the like disclose , for example, a method in which the surface of a substrate is coated with an adsorbed molecule having an amino group (for example, .gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltrimethoxysilane and the like), then this substrate is allowed to react with a functional molecule having a functional group (for example, acid chloride and the like) which can react with the amino group to produce a composite material in which the functional molecule is introduced into the substrate.
However, in this method, there is a problem that the amino group of the adsorption molecule and a hydroxyl group and the like on the surface of the substrate form a hydrogen bond and the function of the amino group is deteriorated, and therefore, only few functional molecules is allowed to react. As a result, the function of a thin film formed on the surface of the substrate can not be sufficiently improved.
Further, Japanese Patent Application Laid-Open (JP-A) No. 5-117624 discloses a method in which a functional group is introduced into a thin film using a silane-based adsorbed molecule having chlorosilyl groups on both end. However, in this case, there is a problem that a hydroxyl group and the like on the surface of the substrate strongly interacts with the reaction group (chlorosilyl group) of a main molecule which reacts with the functional molecule. Accordingly, only few functional molecules are introduced into the substrate. As a result, the function of a thin film formed on the surface of the substrate can not be sufficiently improved.
On the other hand, there is also an attempt in which functional groups are introduced into an adsorbed molecule. However, in this case, molecules to be adsorbed which can be synthesized are restricted due to difficulties in synthetic method. Therefore, function thereof is restricted, and the range of applications of the above-described composite material obtained becomes narrow. And, there is a problem that synthesis is difficult, molecules to be absorbed are synthesized via several synthetic steps due to difficulties in synthesis. As a result, the composite material can not produced at low cost.